United Continental Holdings CEO Oscar Munoz is "currently recovering well" after his Wednesday heart transplant and is still expected to return from medical leave at the end of the first quarter or the beginning of the second quarter, the airline said Thursday.

The update came a day after United's surprise announcement that Munoz, who suffered a heart attack Oct. 15, underwent a heart transplant early Wednesday.

Munoz, who was named United's CEO Sept. 8, has been on medical leave for much of his short tenure at the world's second-largest airline, one with a long list of operational and employee issues to fix. On Thursday, the Chicago-based company and doctors at Northwestern Medicine, where the transplant was performed, sought to reassure employees and investors.

However, transplant experts say Munoz, 57, is likely to spend several tough months recovering, and patients who undergo the procedure are sometimes cautioned to wear masks, avoid crowds and refrain from flying for up to six months to avoid infections. It often takes two to six months before a person can resume a full-time job and normal lifestyle.

"This is a life-changing event," said Dr. Nir Uriel, director of Heart Failure, Transplant and Mechanical Circulatory Support at the University of Chicago."It's not like you go back home after four weeks and go right to work."

Since early December, Munoz had been gradually resuming company-related activities in collaboration with interim CEO Brett Hart, visiting with employees and participating in meetings. He visited United's Chicago operations center on Thanksgiving.

Since the heart attack, Munoz had been "progressing well, with the assistance of an implanted medical device," and a transplant was considered a better alternative to "long-term reliance on the implanted device and was not the result of a setback in his recovery," the company said Thursday. "Munoz had been cleared to return to work prior to the transplant."

"The surgical team was quite pleased with how the procedure went," Dr. Duc Pham, director of the Northwestern Medicine heart transplant program, said in the company's statement. "The patient's early course has been excellent, and the transplanted heart is functioning very well."

Patrick McCarthy, chief of cardiac surgery for Northwestern Medicine, said that given Munoz's "excellent physical condition and the rapid pace of his recovery prior to the transplant," the medical team expects "a quick recovery and a return to his duties as CEO."

Initially, in early November, United said it expected Munoz to return to work full time in the first quarter.

The Cleveland Clinic has performed more than 1,000 heart transplants during the past two decades, including on numerous corporate executives. Many patients returned to work within three months, said Dr. Randall Starling, head of its cardiac transplant program.

"I could see an executive walking into a boardroom in one to two months in a suit and looking relatively good," Starling said.

There aren't many known examples of CEOs who've undergone heart transplants. Vanguard founder John Bogle, now 86, had a heart transplant at age 66 in 1996 after years of hospitalizations for a genetic heart condition. He resigned from his CEO position at Vanguard before the operation and returned to the position of chairman and later director.

Bogle regards his transplant and the 20 years of vitality since then "as a miracle, there's no question about it."

According to the National Heart, Lung and Blood Institute, recovery starts with one to two weeks in the hospital, followed by three months of monitoring by the transplant team at the transplant center.

Patients recovering from transplants take medications to shut down the immune system, which otherwise might try to attack the new heart, which is recognized as a foreign presence in the body. Some doctors advise transplant recipients to take extra precautions and stay away from closed air-circulatory systems, like those on airplanes.

"Economy class has terrible air," said Dr. Valluvan Jeevanandam, chief of cardiac and thoracic surgery at the University of Chicago. "A heart transplant patient should never sit back there."

The first few weeks of recovery can be sharply limiting.

Much depends on how healthy the individual is, along with the person's resiliency and motivation to get well. How much stress a recovering transplant patient can handle afterward also varies.

"After you replace the heart, you have a new engine inside of you," University of Chicago's Uriel said. "I have a lot of patients in very stressful positions, and they don't have any problem going back to stressful situations."

Survival rates seem promising. At the Mayo Clinic, for instance, 96 percent of heart transplant patients survive the first year, and 75 percent survive 10 years.

The news of Munoz's surgery seemed to rattle investors.

United's stock closed down 4.7 percent Thursday, worse than the overall market and some peers.

After the market closed, United filed Munoz's five-year employment contract, which took effect Sept. 8, with the Securities and Exchange Commission.

In addition to a base salary of $1.25 million a year, Munoz became eligible this year for the company's annual cash bonus program and an annual long-term incentive award valued at $10.5 million, provided that he has been in active service for at least six months. The contract also included "sign-on compensation" of $5.2 million, partly to compensate him for stock awards that he gave up at his last employer, rail company CSX.

The contract also said Munoz was expected to become United chairman at or before the company's 2017 shareholder meeting.

In the Thursday announcement, United said Hart, the company's general counsel, would remain acting CEO until Munoz returns.

Morningstar analyst Chris Higgins thought there was an "outside" chance that United might name another interim replacement. Potential replacements, he said, could include Vice Chairman and Chief Revenue Officer Jim Compton or acting Chief Financial Officer Gerry Laderman.

That could be "a positive for the stock in our view given Hart's relative lack of operational experience," Higgins said.

Henry Harteveldt, founder and travel industry analyst for Atmosphere Research Group, said he was shocked to hear of Munoz's heart transplant.

"United had not provided much detail on his condition," he said. "I recognize it's a complex situation because of privacy laws surrounding patient information, but a heart transplant is a serious procedure."

Harteveldt said he wonders whether United was "trying to downplay the real state of Mr. Munoz's health problems."

It's fortunate, he added, that "United is operating reasonably well with its current team in place."

A version of this article appeared in print on January 08, 2016, in the News section of the Chicago Tribune with the headline "United's CEO faces uncertain recovery - Experts say airline chief's work return could take months" —
Today's paperToday's paper | Subscribe